Hood for electric furnace



Aug. 11, 1953 A. o. WILLIAMS ET AL HOOD FOR ELECTRIC FURNACE 10Sheets-Sheet 1 Filed April 1, 1950 AHHH HMH h l H 5 h lM l ll l R l H' ll H o m E v V n m I w r M1 .1! 111 I n N r b 1 a m o a o a m; L m r w Wk w Aug. 11, 1953 A. o. WILLIAMS ET AL noon FOR ELECTRIC FURNACE 10Sheets-Sheet 2 Filed April 1, 1950 r \MMM Y Qu w a m v.M T m0 m FM W Z ry W Aug. 11, 1953 A. o. WILLIAMS ETAL 2,648,714

noon FOR ELECTRIC FURNACE Filed April 1, 1950 10 Sheets-Sheet 3INVENTORS 40014 7 O. W/ZZ/4M5, X V/4171"? G. MCEUIF/VIV,

ATTORNEY 1953 A. o. WILLIAMS ET AL 2,648,714

HOOD FOR ELECTRIC FURNACE ATTORNEY 1953 A. o. WILLIAMS ET AL HOOD FORELECTRIC FURNACE 10 Sheets-Sheet 5 April 1, 1950 W4 75/? G M BOP/V15)ATTORNEY g- 19,53 A. o. WILLIAMS ET AL 2,648,714

HOOD FOR ELECTRIC FURNACE 1O Sheets-Sheet 6 Filed April 1, 1950 WM k 3-aim-m) M l \l a ATTORN EY Aug. 11, 1953 A. o. WILLIAMS ET AL 2,648,714

HOOD FOR ELECTRIC FURNACE Filed April 1, 1950 10 Sheets-Sheet 7INVENTOR5 zxzzzfizzzzxi; L BCY/QMQMLHW ATTORNEY Aug. 11, 1953 A. o.WILLIAMS ET AL HOOD FOR ELECTRIC FURNACE l0 Sheets-Sheet 8 Filed April1, 1950 mama;

INVENTORS WM H /F M a 0 M5 n WM L mw F M u x Aug. 11, 1953 A. o.WILLIAMS ET AL 2,648,714

HOOD FOR ELECTRIC FURNACE Filed April 1, 1950 10 Sheets-Sheet 9 \1INVENTORS 4001/? 0. W/ZZ/4MS, 144417 55 G. MCBC/F/VFV,

. BY Qua/-91 L "\W ATTORNEY Aug. 11, 1953 A. o. WILLIAMS ET AL 2,648,714

I noon FOR ELECTRIC FURNACE Filed April 1, 1950 10 Sheets-Sheet 10 C/KWATTORNEY Patented Aug. 11, 1953 UNITED STATES PATENT OFFICE HOOD FORELECTRIC FURNACE Application April 1, 1950, Serial No. 153,398

Claims.

The present invention relates to an improved hood for calcium carbidefurnaces.

In making calcium carbide, lime (CaO), and coke are fused in an electricfurnace at temperatures ranging from 16003000 C. In this process a greatdeal of carbon monoxide is evolved, which, in the open type of carbidefurnace, is allowed to burn and pass up the stack along with greatquantities of lime and coke dust. In attempts to recover by-productcarbon monoxide and to abate the dust nuisance, the totally sealed typeof furnace has been developed, in which the upper surface is sealed, thelime coke charge is added through openings, and by-product gases anddust are led off through surface ducts. The sealed type of furnace,however, is subject to serious disadvantages, the principal of whichbeing the difficulty experienced in giving proper attention to thecharge to keep it feeding uniformly and prevent formation of a hardcrust. There also is present a large volume of gas under the cover whichconstitutes a serious explosion hazard.

As a compromise between the open and closed type of carbide furnaces,the semi-sealed carbide furnace system of the present invention has beendeveloped. In this furnace, hoods are set between the electrodes andcover only about 45% to 75% of the surface area of the charge. Each hoodis connected to a duct fixed in the furnace wall and by maintaining aslight suction in the duct, about 75% of the carbon monoxide and 85% ofthe dust are led away through the furnace charge and into a recoveryunit. When operating the semi-sealed type of furnace it is important notto use too low a pressure in the ducts; otherwise, air above the furnacecharge will be drawn into the hoods and ducts along with the carbonmonoxide, with consequent loss of carbon monoxide due to burning. Inoperating the semi-sealed furnace, therefore, it is necessary to permitthe escape of a small amount of carbon monoxide, which is allowed toburn at the top of the charge, thereby serving as an indicator of properpressure balance in the duct system.

It is an object of this invention to recover combustible gases indust-free utilizable form from a semi-sealed calcium carbide furnace.Another object is to abate the dust nuisance customarily attending theoperation of a calcium' carbide furnace.

It is also an object of this invention to provide a furnace hood of verylong life, which can be placed in the furnace or removed from it withnegligible loss of operating time. It is a further object to provide ahood, the halves of which are substantially completely electricallyinsulated from each other, and in which water may be excluded from thelower pipes in the event of failure, so that the hood may still beoperated without the necessity of an immediate shut-down.

It is an object of the present invention to provide, in combination, acalcium carbide furnace and accessory hood system, in which thedisadvantages of the sealed furnace are largely eliminated. It is afurther object to provide a hood system for a carbide furnacecharacterized by its simplicity, ease of installation and replacement,and long operating life.

These and other objects will be evident from the description below.

Fig. 1 represents a rear elevation of calcium carbide furnace and showsthe dust collection assembly with two hoods in section.

Fig. 2 is a sectional view of Fig. 1 taken along the line 2-2 andlooking in the direction of the arrows, and shows more clearly the fumescrubbing system with relation to an individual hood. Fig. Z-a is amodification of Fig. 2, showing a fume duct built integrally into thefurnace.

Fig. 3 shows a complete individual hood with the refractory coveringbroken away at the far end to show the piping assembly at that end. Fig.3 also shows the hood assembly at the water supply end.

Fig. 4 shows the hood completely covered with a monolithic layer ofrefractory cement.

Fig. 5 is a plan elevation of the interior piping system of the hood andFig. 6 is a side elevation of the same piping.

Fig. '7 is a rear elevation of Fig. 4 and shows the piping assembly ofthe hood interior. Fig. 8 is a sectional view of Fig. 4 taken along theline 8-8 and looking in the direction of the arrows. Fig. 9 shows thepiping assembly of the hood in relation to the bracing members. Fig. 10shows the method of joining the two halves of the piping assembly inelectrically insulated relationship. Figs. 11, 12, and 13 are sectionalviews of Fig. 10 taken along the lines Il--II, l2-|2, and I3-l3,respectively, looking in the direction of the arrows. Fig. 14 shows aseparated view of the assembly of Fig. 10 and Fig. 15 is a planelevation of the same view.

Fig. 16 represents a plan elevational view of a furnace having theelectrodes arranged in a triangle or delta with the hood and dust recov-3 ery system of the present invention in place, the electrodes beingshown in section.

Fig. 17 shows the underside of an individual delta furnace hood.

Fig. 18 is a side sectional view of Fig. 16, partly in elevation, takenalong the line l8 i8 looking in the direction of'the arrows.

Fig. 19 is analogous to Fig. 16, except that the gases are withdrawnfrom a side exit system. Fig. 19-a shows a means of electrically.insulating the halves of the piping of the hoods of Fig. 19. Fig. 20 isa side sectionalview of. Fig. 19, partly in section, taken along 'th'eline 20'-29, looking in the direction of the "arrows.

Referring to Fig. 1, the hood in cross-section duct 2. The duct entersthe dust scrubbing assembly at 3, which leads to water traps. Up

take duct assembly 5 leads the scrubbed gases into a recovery unit (notshown) or may vent ther'n'to the atmosphere. On either side of thehoods'are' suspended the customary electrodes, such asSoderberg'electrodes or the like (not shown)? Referring to Fig. 2, at 2.is shown the fume duct base"generally. It will be seen that the duct ispositioned over the furnace side Wall 6 and is aflixed to the upperfloor I of the furnaceiroom, extending over the wall into the furnaceproper and down through and under the room floor. While Fig. 2 shows aconvenient means for installing the dust recovery system of thisinvention to an existing calcium carbide furnace without extensivealternations, when, building a new furnace which would incorporate theinvention, it is preferred to build the fume'duct 2 through the furnacewall rather than to buildthe duct over. the furnace wall; and suchpreferred embodiment is shown in Figs. 2'-2a. A clean-out door 8provides access to the interior of the fume duct 2,"a nd"a duct 9,provided to take gases away from furnace during inspectionror repairs tothe gas cleaning assembly, is connected directly to fume duct 2.-t=

Referring to Fig. a, pipe termini is. I i, :2 and l3 (andlfl', II, l2,and 13 in the :other half of'the'assembly) lead'to water connections(not shown) -,-in the furnace room floor. In normal operation waterflows into the pipe assembly at I fl out through l I which is exteriorlyconnected to l2 by cross'piping (not shown), back in through IZ andfinally. out through 13. However, in the eventflaws developin I2 'or 13by reason of burn-out, corrosio'mfor from other causes, wateris'shut'out of the'l'2l3 circu'it'by'turning off their respective valvesand taking all the exit flow from H instead of [3. The same arrangementis followed for thepipes in the other side of the hoOdF-At 4 are showncrane hook tabs for lowering the hood 'into'thefurnace, or for removingit.

The course of water circulation within the hood may be traced in thepiping assemblies as shown in Figs. 5 and 6, ,whichfigures also show ameans of holding inposition the pipes of each subassembly, i. 'e.', bymeansof sectional bracing members with its supporting braces is filledin and cover ed I with refractory brick and mortar as shown. While it isnot absolutely necessary, the life of 4 the hood is sensibly prolongedby coating substantially the whole with a layer of refractory cement toprovide a monolithic surface. Owing to the basic nature of the furnacecharge, it is pre ferred that the brick and mortar be of a basic orneutral character. Brick such as is. use,d in the hearth of a blastfurnaceandacast monolithic refractory similar to that commonly used inboiler settings have been found to give excellent service.

Itv has beenfound that the life of the hood is greatly increased if thewater pipes in opposite halves, of the hoods. are completelyelectrically insulatedfromone, another. An excellent means of doing;this is. shown in Figs. 10-15 inclusive. In these figures, the metalangle extensions 2| and22 ofthe two framing members 23 and 23-aaresepar'ated by a thick heat resistant dielectric 25,.suchas compressedasbestos, or asbestos mixed with Portland cement and then compressedinto theangle shape shown. The three angl S: are bolted together using adielectric assembly -,of washers and bushi ng ,as shown at, 25 in Fig.12. The crane tab !4.- is preferably attached .to,,the assembly at thispoint, asbywelding .or the like.

When used with a rectangular carbide furnace, thehoods are lowered intoplace between theifure nace electrodes. The lime-cokeichargeeis thenbuilt up around the hoods by-meansof, the ,cus: tomary overheadlfeeders,and preferably .spread over the hoods to a depth of several-inches By sosubmerging the hoods in the charge,.-the,flow of gases within the chargeis more easily-regulated The suction assembly.3 of Fig... 1 is ad:juste'd so that only a slight flame. burns around the electrodes,indicating that almost allgasesare being drawn off through the.scrubbing system. It is preferred to maintain a smalhamount ofcombustion above the. charge. as ;..a convenient means of showing thatno ,air..is being drawn down through the: charge, and into the hoods.Such air wouldburn. and/or,dilute the gas. .or might create an explosionhazard in the recovery system. A pressure differential, of vabout ().2mm. of. mercury from atmospheric pressure will ordinarily suffice toaccomplish the.,des iredyaouum. though obviously, this figure ;1nay,.yary from .installation, to installation.

The excellent results .obtai n ed withpthe hood of this invention areattributable in parttothe fact that'it may. be lowered into positionwithout 'boltng or other fastening, andthat its two .coo l.-

i'ng' assemblies arev completely electrically. insulated from. oneanother, thus. eliminating .oven heating by Vagabond currents..-

The operation of the hood in ,connection w ith the. delta furnace isanalogous to. the, -abov. e ,described operation oftherectangularfurnace.,

Referring to Fig. 16 at. lfivl is shown generally a delta furnace of anywell lgnown,type... .A l.,l02, E02. and H02". are shown thecustomarycarbon electrodes At W3, W3. andfiilill' are thethree leaves of the hoodsystem. At ,Hl=i.and jt 5,l,,and lll i'and I 05' are shownentrance andexitwaterr cooling pipes, respectively, ,for, the .respective halves ofhood 163. At mliis shown the center exit duct, which is provided ,with afiarug eJill, which supports the center edges of thehoods. Thecenterexit duct Hi6 is itself supported from the ceiling orby other overheadsupportthrough ass'emblyWOB, shown best in Fig. 18.- 4 At {094s shown,in section, an erect dust recovery-pipeor column (shown best in Fig. 18)equipped-at H0 with an atmosphericvent valve-of any-customary design,such as the butterfly: type. Dust-recovery pipe l-llflileads downwardto'suctionmeansl-liof any well known type, such as a power fan, and

terminates in water trap II2, (not shown in Fig. 16 but shown in Fig.18). The operation of the hood system and dust recovery system will beevident from the foregoing description. The dust-laden gases arecollected by the hood system I03, I03 and I03", and are drawn throughcenter exit duct I06 into dust recovery I09, III and H2. The upperportion duct I09, with valve IIO (shown best in Fig. 18), is provided totake gases away from the furnace during inspection or repairs to thedust recovery system.

Despite the relatively large interstices between the hood leaves, arelatively small amount of gas and dust is lost through these openings.It has been found that the flow of the fumes can be controlled with avacuum amount to about 0.3 inch of water, leaving only a very smallflame to burn in the interelectrode open areas. Obviously this figuremay vary according to the installation.

The center exit dust recovery system described above, together with thefour-pipe cooling system for each hood leaf, is preferred to the sideexit system with a two-pipe cooling system, illustrated in Figs. 19 and20, and described below.

In Fig. 19, there is shown at Illl the furnace generally, withelectrodes I02, I02 and I 2". The three side-exit-type hood leaves at II3, I I3 and II3" are shown resting on the furnace edge and on centerflange support I01. Gases collected by the hood are drawn off throughside exit ducts II I, thence into exhaust manifolds I I5 and II 5, andthence into secondary collectors IIS and H6. Central duct II'I (shown inFig. 20), integral with flange I01, is suspended from overhead andcarries valve H8, normally closed, but which may be opened to vent thegases into the atmosphere when the dust collecting system is shut downfor repairs or the like. The secondary collectors I I6 and I I6 areunited in coupling II9, beneath which is dustrecovery col-.

umn I09, with its accompanying suction fan II I and water trap II2. Saiddust recovery column and accessories are not shown in Fig. 19, but areshown in Fig. 20; they are analogous to the dust recovery assembly ofFig. 18.

Fig. 19-41 shows a means of electrically insulating the two halves ofthe piping of each hood in Fig. 19. At I20 is shown the pipe, bearingflange I2 I. The respective flanges are joined in abutment to refractoryelectrical insulating gasket I22 by means of bolts I24 inserted throughrefractory insulating sleeves I23.

Hood structure for delta furnace The individual hood leaf is formedessentially of monolithic refractory cement, preferably of a basiccharacter, such as that used in boiler settings, as a covering over thepiping framework, as shown in Fig. 17. As shown therein, a preferableembodiment of the invention is to form the hood of refractory brick atthe points of greatest abrasion, as where the hood rests on the furnaceedge and on the center support flange. The hoods need not be providedwith semipermanent fastenings for bolting to the furnace. It is, infact, a primary advantage of the invention that the hood may be put inplace and removed without being fastened or unfastened to or from thefurnace structure. It is further preferred, in building the hood, toinsulate the pipe skeleton electrically, as by coating same withrefractory cement or the like.

The pipes sections are insulated from each other with insulatingrefractories where joined in the structure, and externally by rubberconnections. It is essential that each half of the individual hoods bethoroughly electrically insulated from the other, the furnace, and theelectrodes. Otherwise, stray currents tend to overheat the hoods andreduce hood life. A method of insulating the two halves of the piping ofFigs. 19 and 20 by means of a refractory gasket is shown in Fig. 19-a.

With either of the two modifications, central exit and side exit hoods,the furnace is charged in the same manner. The lime-coke charge isdropped through overhead feed means, customary in the carbide furnaceart, into the interhood spaces. In using large delta furnaces, it ispreferred to build up the charge so that the hoods are immersed in it toa depth of a few inches. This has the effect of reducing the escape ofdust and gas. In smaller delta furnaces, it is not necessary to bury thehoods, as the proper suction can be maintained without excess loss ofgas.

It may be noted that the piping contours within the hoods in Figs. 1620is largely arbitrary, and that any configuration of the cooling pipingis satisfactory so long as it provides the necessary cooling. A'morevariegated contour such as that of Figs. 19 and 20 will naturallyprovide more cooling effect and greater support to the hood than that ofFigs. 17 and 18.

While the invention has been described with particular reference tospecific embodiments, it is to be understood that it is not to belimited thereto but is to be construed broadly and restricted solely bythe scope of the appended claims.

We claim:

1. An interelectrode hood adapted to seat freely on a fume duct of anelectric furnace for the preparation of calcium carbide, said hoodcomprising an upper surface with downwardly extending sides containingpaired assemblies of spaced heat resistant pipes, said assemblies beingelectrically insulated from each other and being adapted to circulate acooling medium and being substantially covered with a refractorymaterial; the hood sides extending downward far enough that when thehood is in place on the normally operated furnace, the hood sides areimmersed in the furnace charge, whereby a vapor collection zone isprovided within the hood.

2. The hood according to claim 1 in which one end consists of aflattened edge rest adjacent to a dropped shoulder, said edge beingadapted to sit on an abutting support on the carbide furnace wall, theother end of the hood having a shape adapted substantially to cover afume duct at the opposite furnace wall.

3. The hood according to claim 2 in which each of the paired pipeassemblies comprises at least two sub-assemblies arranged to permit theexclusion of cooling medium from any of the said sub-assemblies.

4. The hood according to claim 3 in which one end comprises a flattenededge rest adapted to sit on one edge of the furnace wall, and the otherend is shaped substantially to cover a frame duct in the oppositefurnace wall; each of said paired pipe assemblies comprising twosubassemblies, an upper and a lower, arranged to permit exclusion ofcooling medium from each of said sub-assemblies.

5. In combination, an electric furnace for the preparation of calciumcarbide comprising an open vessel, a plurality of spaced electrodes de-'pending :into the same, 'nd' a :plura y" of fume ducts a plurality; ofxhoods positioned between the said electrodes-"so asito coverabout45-75%of thevfurnace surface, said hoods" being positionediseparably onsaidfume ducts-each of said hoods" comprising an upper surfacewith;sides extending downward farenoughso that thesaid sides are immersed inthe furnace charge during furnace operation; "said sides containingvpaired assemblies f spaced, heat resistant pipes'xadap'ted to circulatea cooling: medium; "said *pairs being electrically insulated :from eachother la l ldgbeiilg substantially covered with a*fefractoryfm'aterialresistant to calcium carbide furnace conditions means for.supplyinga"circulating cooling me dium' to the i said gcooling pipes;Randi suction means for drawing fumes from the said fume duct's- 1 4 R17; 5 i, H- 2 Hi 6. :An interelectrdde .hodd rforf a1 delta-type electricfurnace; saidhood -"co'mprisii1g.:acover with downwardly-extendingsides, the whole theing formed ofarefractoryimaterial resistant tofurnace' conditions' supported by a framework of tempefature re'sistan'ts pipes, '1 said i pipes being adapted'to circulate cooling-'vmedium andbeing protected withrefractory electrical insulation; "the hood sides'being'ispac'd; from adjacent electrode position's and" extending-.substantially from the -furhac'center to the furnace periphery; thehood sides extending downwardly so that whenthe'hood is in place on thenormally operating furnace; the? hood sides are immersed :in thefu'rnacecharge',"-whereby' a vapor collectior'i'z'one is provided withi'r'1 thehood.

7. The hood according to claim 6 in the 1 sition'd electrodes 9dependinginto -sa'me', and

fume duct means; three hoods,- positioned between'the"saidelectrodes, soas to cover about 45-75% of the furnace surface, said hoodsbeingsupported by'the furnace periphery and support means at the center ofthe furnace surface; each of the said hoods being positioned separablyon the said fume duct means, and each of ,thesaid hoods comprising anupper surface with sides extending downward far enough'so that the saidsides are immersed in the furnace charge during furnace operation, saidsides containing paired assemblies of spaced heat resistant pipesadapted to circulate a cooling medium, said pairs. being electricallyinsulated from each other and being substantially covered withiarefractory material resistant to calcium carbide furnace conditions;means for supplying a circulatingcoolingmedium to the said pipes; andsuction meari'sIfor drawing fumes from the said fume duct means.

91 The Hood according to claim 8 in which the suctionmeans is connectedto a central confiuence of the hoods; .c 1'

-10. The hood according to :claim. 8v in which the suction meansisconnected to the hoods at the furnace periphery. t.

AUDLEy o.-wILLI A1Vfs WALTER G. MCBURNEY.

Renate; Cited inthjefilefo f th s patent UNITED STATES PATENT h DatNumber Name 572,312" Price Dec. 1, 1896 826,744 Price r July 24, 19061,635,819 Corcoran i 'Ju1 y12, 1927 1,92'2L312' Mansfield Aug 15, 19331,992,465 Blagg Feb. 26, 1935 2,222,004 Smith -QNOVQ 1 9, 1940 2,286,732Hardin c June 6, 1942 2,426,643 Rid'gway Sept; 2,1947 2,448,886 Hopkins;Sept. 7, 1948 v FOREIGN PATENTS I Number J Country Date 443,994 FranceOct. 7, 1912

